The present application relates to a surface emitting device, a liquid crystal display, and an optical sheet combination, all having both a light converting function and a specific polarization split function.
Liquid crystal displays (LCDs), which have lower power consumption and which can also he made smaller and thinner in structure compared with CRTs (Cathode Ray Tubes), are presently used extensively in various sizes for equipment ranging from small devices, such as portable telephones, portable game machines, digital cameras, and PDAs (Personal Digital Assistants) to great-sized liquid crystal television sets.
The LCDs are classified into a transmissive-type, a reflective-type, and the like, and particularly a transmissive-type LCD includes a liquid crystal display panel, a first polarizer (polarizer plate) disposed on a light incident side of this liquid crystal display panel, a second polarizer (polarizer plate) disposed on a light emergent side of the liquid crystal display panel, and additionally a backlight unit as a light source. There are a direct-below type backlight unit and an edge-type backlight unit. The edge light type backlight unit is constructed of a lightguide plate disposed on the back of the liquid crystal display panel, a light source disposed on one side end of this lightguide plate, a reflector plate that covers a surface opposite to a light emergent surface of the lightguide plate, and the like.
As light sources used for these types of backlight units, CCFLs (Cold Cathode Fluorescent Lamps) emitting white light have hitherto been widely used. Particularly in recent years, backlight units using LEDs (Light Emitting Diodes) as a light source are considered potential for mobile applications such as portable telephones.
In displays for mobile applications, a proper level of luminance in the front direction is required, and techniques for restricting a backlight emerging direction to the front direction have been adopted therefor. For example, in order to align the backlight emerging direction with the front direction, it is known to arrange an optical sheet called a brightness enhancement film or brightness enhancement sheet between a backlight unit and a liquid crystal display panel (see Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-544565 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 2004-168869 (Patent Document 2)).
The brightness enhancement film is formed of a prim sheet having triangular prisms cyclically arrayed at a small pitch on one surface thereof, and has a function of converting backlight's light by directing them toward the front. Particularly, configurations are known, in which two prism sheets are stacked one upon another with their prism extension directions oriented orthogonal to each other, and in which a reflective polarizer sheet is disposed on a prism sheet, the reflective polarizer sheet transmitting one linear polarized component therethrough and reflecting the other linear polarized component therefrom (see Patent Document 1).
The prism sheet is formed typically by laminating curable resin layers, formed of an active energy beam-curable resin, on a surface of a transparent substrate (see Patent Document 2).
In the displays for mobile applications, there is an increasing demand for reduction in the thickness of the display as a whole and higher image quality in recent years. However, the reflective polarizer sheet used to enhance the front luminance is expensive, thereby elevating the manufacturing cost of a liquid crystal display. In addition, use of the reflective polarizer sheet increases the number of sheets, thereby preventing the reduction in the thickness of the liquid crystal display. Furthermore, even using the reflective polarizer sheet, a part of polarized component in an absorption axis direction of a first polarizer is leaked, whereby the function is not always be enough.